receivingVb not set in noteVbContentAvailable

There is a typo in sample adapter sources: receivingVb is not set when Adapter::Xaction::noteVbContentAvailable is called. Modifying and pass-through adapter samples are affected.

The bug is probably harmless under most conditions because these simple adapters are using receivingVb for state checking and the checks seem to work even if the last assignment is not performed. However, it is impossible to say for sure.

The attached patch fixes the problem. The fix will be available in the next release.